President Donald Trump warned that a new migrant caravan is forming in Honduras and only a wall or steel barrier will keep the U.S. safe, as a row over funding for his key project has kept the federal government partially shuttered for more than three weeks.

Democrats led by House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer have blocked congressional funding for the wall, which Trump had vowed Mexico would pay for during his presidential campaign, prompting the longest shutdown in U.S. history.

"A big new Caravan is heading up to our Southern Border from Honduras. Tell Nancy and Chuck that a drone flying around will not stop them," Trump said on Twitter Tuesday. "Only a Wall will work. Only a Wall, or Steel Barrier, will keep our Country safe! Stop playing political games and end the Shutdown!"

He followed up an hour later, writing on Twitter: "Polls are now showing that people are beginning to understand the Humanitarian Crisis and Crime at the Border. Numbers are going up fast, over 50%. Democrats will soon be known as the Party of Crime. Ridiculous that they don’t want Border Security!"

Trump has repeatedly sought to highlight the formation of a new group of migrants in recent days, as the White House has looked for ways to ratchet up pressure on congressional Democrats and divert attention from other recent news reports.

The New York Times reported last week that the FBI in 2017 started investigating whether Trump had been working on behalf of Russia against U.S. interests. The Washington Post reported Saturday that Trump confiscated notes from his translator after meeting with Russian President Vladimir Putin.

While three-quarters of the federal government has been funded for the time being, the shutdown has impacted more than 800,000 federal workers and caused security screening lanes to close at airports in Miami and Houston.

“There is another major caravan forming right now in Honduras, and so far we’re trying to break it up, but so far it’s bigger than anything we’ve seen,” Trump said Thursday. “And a drone isn’t going to stop it and a sensor isn’t going to stop it, but you know what’s going to stop it in its tracks? A nice, powerful wall.”

He reiterated his concerns in a Saturday phone interview with Fox News, and said the U.S. was able to prevent migrants from a caravan he highlighted during the midterm elections from entering the country because of the existing wall on the border between Tijuana and San Diego.

'They couldn’t get through because we have a wall there,' Trump said.

And in a speech Monday in New Orleans, Trump complained that the governments of Honduras, El Salvador and Guatemala hadn’t done more to prevent migrants from heading toward the U.S.

“Like so many nations, we help them, they don’t help us,” he said.

The focus on the group of migrants mirrors the president’s efforts ahead of the midterm elections, when he issued daily warnings that a group of several thousand migrants that was slowly making its way north from Mexico’s border with Guatemala would bring disease and crime to the U.S. Trump also claimed that the caravan had been funded by political opponents and contained terrorists, though later conceded he did not have evidence to support the terror claim.

Trump threatened to close the U.S. border with Mexico to prevent those in the caravan from illegally entering the U.S. He later raised the prospect of using the military to build the wall absent Democrats complying with his request for $5.7 billion for its construction.

President Donald Trump warned that a new migrant caravan is forming in Honduras and only a wall or steel barrier will keep the U.S. safe, as a row over funding for his key project has kept the federal government partially shuttered for more than three weeks.